#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

using namespace std;

using ll = long long;

class Solution {
public:
    int tribonacci(int n) {

        if (n == 0)
            return 0;

        if (n == 1 || n == 2)
            return 1;

        vector<int> dp(n + 1);
        dp[0] = 0;
        dp[1] = 1;
        dp[2] = 1;

        for (int i = 3; i <= n; i++) {
            dp[i] = dp[i - 1] + dp[i - 2] + dp[i - 3];
        }

        return dp[n];
    }
};

class Solution {
public:
    int waysToStep(int n) {
        vector<long long> dp(n);

        const int x = 1000000007;
        if (n == 0)
        {
            return 0;
        }
        if (n == 1)
            return 1;
        if (n == 2)
            return 2;

        dp[0] = 1; dp[1] = 2; dp[2] = 4;

        for (int i = 3; i < n; i++)
        {
            dp[i] = (dp[i - 1] + dp[i - 2] + dp[i - 3]) % x;
        }
        return dp[n - 1];
    }
};

int main()
{
	

	return 0;
}